Vehicles operating in an autonomous mode (e.g., driverless) can relieve occupants, especially the driver, from some driving-related responsibilities. When operating in an autonomous mode, the vehicle can navigate to various locations using onboard sensors, allowing the vehicle to travel with minimal human interaction or in some cases without any passengers.
Vehicles can navigate using reference lines. A reference line is a path that autonomous driving vehicles should drive along when there are no surrounding obstacles. A smooth reference line can lead to more stable vehicle control. Furthermore, smoothness of a path planning trajectory, which also depends on the smoothness of the reference line, and/or smoothness of a speed planning trajectory which include obstacle and/or traffic information perceived by the vehicle can lead to more stable vehicle control.